When I first started looking for my Forths I extracted a lot of information on Forths in Wayne Co., IL. In the 1860 c there is a William A. Forth m. to Eleanor. He looks to be 56 and she, 34. There are 8 children listed including a Mildred, age 7 (could be a Millie) and also a M----A. age 17. This c. is in Wayne Co., Brush Creek Twp. pg 123.
The index for the 1860 c. shows the following: Abraham, James M.,3 John's, Levi, Robert T., and 2 Wm. A.'s.
I got this information from the Indiana State Library. I also have a note that a Polly Forth was divorced from a William. Maybe this is your line of Forths. Pat